**3.1 Degradation period test**

274 Biogas

Biogas residue fibre film samples were prepared with the method of clean pulping and paper-making process. The optimization of the technological parameters were studied by the method of the central composite quadratic orthogonal rotational experiment, beating degree, grammage, rosin, bauxite and wet strength agent were selected as input variables, and dry tensile strength, wet tensile strength, degradation period were chosen as response

Factors and its levels of experiment were shown in table 3-1. Experimental plan and results

Rosin /%

Factors Response functions

Dry tensile strength N

Wet strength agent %

Bauxite /%

/%

Wet tensile strength N

Wet strength agent

Degradation period day

**3. The study on manufacturing technology of biogas residue film** 

Grammage /g/m2

zj x1 x2 x3 x4 x5 γ(+2) 50 110 1.2 6 3.0 (+1) 45 95 1 5 2.4 (0) 40 80 0.8 4 1.8 (-1) 35 65 0.6 3 1.2 -γ(-2) 30 50 0.4 2 0.6

> Rosin %

Bauxite %

 x1 x2 x3 x4 x5 y1*i* y2*i* y3*<sup>i</sup>* 1 35 65 0.6 3 2.4 29.8 12.0 26.7 2 45 65 0.6 3 1.2 24.2 9.9 25.9 3 35 95 0.6 3 1.2 33.0 15.1 30.3 4 45 95 0.6 3 2.4 35.8 17.4 34.1 5 35 65 1 3 1.2 18.3 9.5 26.5 6 45 65 1 3 2.4 20.3 10.7 27.8 7 35 95 1 3 2.4 35.4 15.7 30.1 8 45 95 1 3 1.2 30.1 16.1 30.1 9 35 65 0.6 5 1.2 23.1 9.6 20.6 10 45 65 0.6 5 2.4 25.5 11.0 27.9 11 35 95 0.6 5 2.4 30.9 18.0 38.3 12 45 95 0.6 5 1.2 35.2 9.8 33.3 13 35 65 1 5 2.4 20.1 11.1 29.5 14 45 65 1 5 1.2 23.0 9.0 20.1 15 35 95 1 5 1.2 32.9 13.0 32.1 16 45 95 1 5 2.4 35.5 17.0 38.9 17 30 80 0.8 4 1.8 26.3 14.7 30.5 18 50 80 0.8 4 1.8 23.4 12.0 31.1 19 40 50 0.8 4 1.8 18.0 9.7 25.0

functions.

Factor level

Run

were shown in table 3-2.

Beating degree SR°

/SR°

Beating degree

Table 3-1. Factors and its levels of experiment

Grammage g/m2

> The arrangement of the degradation period test was shown in Fig.3-1. Degradation state of film samples during degradation period was shown in Fig.3-2

Fig. 3-1. The arrangement of the degradation period test

Study on Manufacturing Technology and Performance of Biogas Residue Film 277

Importance

Wet tensile strength (N)

Degradation period (D)

**3.2.2 Analysis of importance of various factors on response functions**  Importance of various factors on response functions was shown in table 3-3.

Beating degree 1.645 1.046 0.905 Grammage 1.838 1.323 2.341 Rosin 1.094 1.333 0.931 Bauxite 1.344 1.951 2.099

agent 1.526 2.839 2.253

Fig.3-3 showed the effect of beating degree and bauxite on dry tensile strength when other factors were held at 0 level. With the increase of beating degree and bauxite, dry tensile strength firstly increased and then slowly decreased, the maximum occurred when the two factors were held at 0 level. The reason was that with the beating degree increased, the fibre sub-wire broom degree was high, the exposure of hydrogen bonding of the fibre surface increased, the bonding forces between the fibres enhanced, so that the film strength increased; when beating degree was more than a certain value, the single fibre strength was destroyed, the bonding force decreased, led to the decrease of strength, adding bauxite

Fig. 3-3. Response surface and contour plots for the effects of beating degree and bauxite on dry tensile strength: grammage was held at 80 g/m2 and rosin was held at 0.8%, wet

Dry tensile strength (N)

**3.3 Effect of interaction factors on dry tensile strength** 

**3.3.1 Effect of beating degree and bauxite on dry tensile strength** 

excessively to strength had side effect, thus resulting in strength decreased.

Source

Wet strength

Table 3-3. Importance of each factor

strength agent was held at 1.8%

**Bauxite %**

(a)part of film samples after 20 days (b) part of film samples after 35 days (c) part of film samples after 50 days Fig. 3-2. Mulching degradable process in the different time during the period of degradation

The fibre film of biogas residue for degradation discovered that the appearance and performance of the samples changed a lot because of light, air temperature, air humidity, wind, rain and other weather factors, coupled with the soil temperature, humidity, combined effect of microorganisms. According to the observation, the degradation was divided into several stages, initially, the sample surface appeared holes or small cracks, called induction period of the film degradation; over time, holes and cracks gradually expanded, the edge glued to the soil surface, the role of soil microorganisms on the film samples increased, resulted in an increasing number of small holes, broken into fragmentation period of the film samples, the film samples effected by various types of micro-organisms would become increasingly thin, the mechanical strength decreased gradually, until the film entered into the fast degradation period of the samples. Especially, after rain, the increasing of air humidity and soil humidity would make mechanical strength of the samples decrease rapidly, so soil moisture is an important impact factor of the film degradation.

During degradation of the film, the dry tensile strengths were regularly measured, according to scatter, the trends of dry tensile strength (N) and date (d) were available, according to trend line, the time of dry tensile strength at zero of each group was estimated, which was defined degradation period. The result was shown in table 3-2.
